Refrigerant compressor with overload protector

ABSTRACT

A compressor having a sealed housing provided with a bottom compressor unit compartment and an upper motor compartment. A compressor unit is received in the bottom compartment and a motor is received in the motor compartment for driving the unit. The motor comprises a rotor and a stator having a winding the bottom portion of which is positioned adjacent to the bottom of the motor compartment. Connected to the compressor unit is an inlet for the flow of low pressure refrigerant gas discharged from the refrigerator system. A desuperheating coil provides a conduit for the flow of compressed refrigerant gas from the compressor unit back to the housing where the cooled gas enters at a point adjacent to the bottom of the motor compartment. Mounted on the bottom portion of the stator winding and positioned in the path of flow of the gas from the desuperheating coil is a thermostatic switch which is serially connected with the motor and its source of energy. The switch is operable to disconnect the motor from its energy source when the switch senses a combined temperature and current above a preselected value indicative of a motor overload.

United States Patent [191 Anderson [11] 3,874,187 451 Apr. 1, 1975 REFRIGERANT COMPRESSOR WITH OVERLOAD PROTECTOR [75] Inventor: Thomas J.Anderson, North Brunswick, NJ.

[73] Assignee: Fedders Corporation, Edison, NJ.

Primary Examiner-Meyer Perlin Anorney, Agent, or FirmRyder, McAulay,Fields, Fisher & Goldstein [57] ABSTRACT A compressor having a sealedhousing provided with a bottom compressor unit compartment and an uppermotor compartment. A compressor unit is received in the bottomcompartment and a motor is received in the motor compartment for drivingthe unit. The motor comprises a rotor and a stator having a winding thebottom portion of which is positioned adjacent to the bottom of themotor compartment. Connected to the compressor unit is an inlet for theflow of low pressure refrigerant gas discharged from the refrigeratorsystem. A desuperheating coil provides a conduit for the flow ofcompressed refrigerant gas from the compressor unit back to the housingwhere the cooled gas enters at a point adjacent to the bottom of themotor compartment. Mounted on the bottom portion of the stator windingand positioned in the path of flow of the gas from the desuperheatingcoil is a thermostatic switch which is serially connected with the motorand its source of energy. The switch is operable to disconnect the motorfrom its energy source when the switch senses a combined temperature andcurrent above a preselected value indicative of a motor overload.

6 Claims, 2 Drawing Figures REFRIGERANT COMPRESSOR WITI-I OVERLOADPROTECTOR This invention relates generally to a refrigerant compressorand, more particularly, pertains to a refrigerant compressor having animproved overload protector whereby faster and more accurate responsesto overload conditions are obtained.

Motors used to drive compressor units in hermetically sealed refrigerantcompressors are peculiarly subject to thermal overloads which might welldamage the motor winding insulation, thereby resulting in shortcircuits. When such damage occurs, the compressor must be replaced andthe cost of such replacement is usually expensive since a great deal oflabor is required to replace a compressor in addition to the cost of thecompressor per se.

Accordingly, various overload protection arrangements have been used toprotect motors from thermal overloads of the type under consideration.In one arrangement typically referred to as a rotary compressor, themotor windings are cooled by positioning the windings in the path of therefrigerant gas as the gas flows from the compressor unit to therefrigerating system. While this arrangement provides the requisitecooling when the motor is operating properly, a problem is presented ifthe motor stops operating as, for example, when the rotor locks. Themotor will then quickly overheat with consequent damage to the windinginsulation.

Another arrangement commonly used is to provide a thermal cut-out orthermal overload protection device in the form of a thermostatic switchof conventional construction that is connected in series with the motor.The switch is operable to disconnect the motor from its source of energywhen the temperature in the housing rises above a preselected levelcorresponding to an overload condition. However, these thermalprotection devices have proved to be inefficient in the pastparticularly in the case of a so-called non-start condition becauseofthe long interval required for the ambient temperature to reach theoverload temperature. Therefore, an overload condition may be permittedto exist for a substantial time before the device operates.

To be more specific, since the normal operating temperature of a rotarycompressor is relatively high, the temperature at which the thermalprotection device is set to cut-out is likewise correspondingly inexcess of such normal operating temperature. When the compressor isinitially energized it is at substantially the temperature of theenvironment. If a non-start condition is encountered (ie. the motorfails to operate), the temperature within the housing will increase.However, since the thermal protection device cut-out point is setrelatively high, the motor will be subjected to excessive elevatedtemperatures for a relatively long period of time. It is obvious thatcontinued repetition of this sequence of events will have a destructiveeffect on the motor windings over a period of time.

The above problem is compounded by the fact that under operatingconditions a temperature gradient exists within the housing with thehigher temperature at the top of the housing and a lower temperature atthe bottom. Thermal protection devices of the prior art, such as shownin US. Pat. No. 2,946,203, are positioned at the top of the housing and,therefore, must be .set at a relatively high cutout or operatetemperature top of the housing otherwise the motor will be prematurelydisconnected from the source of energy. As a result, the reaction timeof the switch for a non-start condition or the like is correspondinglyincreased.

Accordingly, an object of this invention is to provide an improvedoverload protector for a refrigerant compressor motor.

A more specific object of the present invention is to provide anoverload protector for a compressor that reacts relatively quickly tooverload conditions.

Another object of the invention is a provision of an overload protectorfor a compressor that is highly sensitive to the temperature of themotor windings to be protected.

A further object of the invention resides in the novel details ofconstruction that provide an overload protector of the type describedfor a refrigerant compressor that permits operation of the motor atlower terminal voltages than systems used heretofore.

In accordance with the present invention, a compressor is provided thatcomprises a sealed housing having a compressor unit disposed within alower compressor unit compartment and a motor positioned above thecompressor unit in an upper motor compartment and connected in drivingrelationship therewith. The motor includes a rotor and a stator providedwith a winding having a bottom portion which is positioned adjacent tothe bottom of the motor compartment. A compressor inlet is provided forintroducing low pressure refrigerant gas from the refrigerating systeminto the compressor unit and conduit means provides for the flow ofcompressed refrigerant gas from the compressor unit into the motorcompartment. A housing outlet provides a path for the discharge of thecompressed refrigerant gas from the housing back to the refrigerationsystem. Thermally responsive switch means is mounted adjacent to thebottom of the motor compartment and is connected in electric circuitwith the motor for disconnecting the motor from a source of potentialwhen the switch means senses a temperature above a preselected value,thereby to protect the motor from damage due to overload conditions.

Other features and advantages of the present invention will become moreapparent from a consideration of the following detailed description whentaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a front elevational view, partially in crosssection andpartially in diagrammatic form, of a refrigerant compressor constructedaccording to the present invention; and

FIG. 2 is a schematic circuit wiring diagram of the compressor motor andoverload protector.

A refrigerant compressor constructed according to the present inventionis designated generally by the reference character 10 in FIG. 1 andcomprises a hermetically sealed housing designated generally by thereference charcter 12. The housing 12 comprises a cylindricalintermediate section 14, a bottom dome section 16 and a top dome section18. Peripheral portions adjacent to the bottom edges of the domesections 16 and 18 are received within the cylindrical section 14 andare welded thereto so that the interior of the housing 12 isheremetically sealed from the external environment.

A mounting bracket 20 extends across the interior of the housing 12 anddivides the housing into a lower compressor unit compartment 2.2 and anupper motor compartment 24. As shown in FIG. 1, the mounting bracket isspaced from the bottom of the housing 12 by a distance approximatelyequal to one-quarter of the overall height of the intermediate section14. Mounted on the bottom surface of the bracket and received within thecompressor unit compartment 22 in the bottom of the housing is acompressor unit 26. The compressor unit 26 is conventional inconstruction and is operable to compress refrigerant gas discharged fromthe refrigerating system.

Received within the motor compartment is a motor, illustrateddiagrammatically at 28, which includes a rotor 30 and a stator windings34. Connected to the rotor 30 is an output shaft 36 which connects withthe compressor unit 26 to drive the unit. The stator windings 34 includea top portion 38 and a bottom portion 40 which is positioned adjacent tothe bracket 20 at the bottom of the motor compartment 24.

An inlet tube 42 extends through the wall of the housing 12 into thecompressor unit 26 and provides a path for the discharge of low pressurerefrigerant gas from the refrigeration system (not shown) to thecompr-essor unit. Compressed refrigerant gas from the compressor unit 26is discharged through a conduit 44, which extends through the wall ofthe housing 12, into an inlet tube 46 of a desuperheater coil 48. Thecompressed refrigerant gas flows through the desuperheater coil 48 andis discharged from a desuperheater coil outlet tube 50 into the motorcompartment 24 of the housing 12 through a wall passage 52. As shown inFIG. 1 the discharge opening of the passage 52 is positioned near thebottom ofthe motor compartment adjacent to the bottom portion 40 of thestator winding 34. The desuperheater coil 48 is conventional inconstruction and is operable to cool the refrigerant gas passingtherethrough. For example, in an actualponstruction, the desuperheatercoil has cooled compressed refrigerant gas flowing into the inlet tube46 at a temperature of 235F. to 160F. as the gas flows out of the outlettube 50. I

The gas flowing into the motor compartment 24 through the passage 52flows upwardly across the motor 28 therby cooling the motor. Centrallypositioned in the top dome 18 of the housing 12 is a discharge tube'54that provides a path for the discharge of the compressed refrigerant gasfrom the motor compartment 24 to the refrigeration system. Thecompressed refrigerant gas flows through the refrigeration system toprovide cooling and is discharged back to the compressor unit 26 throughthe inlet tube 42 in the conventional manner. I

As'not'ed hereinabove, a temperature gradient exists within the motorcompartment 24. The highest temperature exists at the top of thecompartment and the lowest temperature is at the bottom of thecompartment. Heretofore, overload protectors have been positionedadjacent to the top ofthe motor compartment and must therefore operateat elevated temperatures. In order to sense a thermal overload, thecut-out point or point of operation of the overload protector must beset relatively high. As a result, the response of the protection devicehas been relatively slow'since a substantial interval of time existsbefore the ambient temperature of the device rises to the overloadtemperature point, particularly with regard to a non-start condition (atthe initiation of a cycle of operation).

In accordance with the present invention, an overload protector oroverload protection device 56 is provided which is located adjacent tothe bottom of the motor compartment 24. The overload protector may beany of the well known types of thermal protection devices which are nowon the market and which are operable to open a switch when the ambienttemperature due to the motor current flowing through the device and thetemperature of the motor windings reach a preset cutout point ortemperature level. The switch is usually serially connected between themotor source of energy and the motor so that the device effectivelydisconnects the motor from its source of energy when the protectiondevice operates.

More specifically, the overload protector 56 is mounted on the bottomportion 40 of the stator winding 34 as shown in FIG. 1. By sopositioning the overload protector 56, a number of advantages areobtained. In the first place, by placing the overload protector directlyon the stator winding 34, the sensitivity of the overload protector towinding temperature is increased. That is, since the overload protectoris in direct heat exchanging relationship with the winding 34, theprotector immediately senses the winding temperature.

Additionally, by locating the overload protector 56 in the bottomportion of the motor compartment 24, the cut-out point of the overloadprotector may be set for a lower temperature than if the protector werelocated in the upper portion of the compartment. That is, since atemperature gradient exists from the top to the bottom of the motorcompartment 24, the temperature at the bottom of the compartment due toan overload condition will be lower than the corresponding temperatureat the top of the compartment.

Moreover, in addition to locating the thermal protector 56 at the bottomof the motor compartment, the protector 56 is also positioned adjacentto the discharge opening of the passage 52. In other words, theprotector is located directly in the path of the cooled compressedrefrigerant gas from the desuperheater coil 48 which further serves tolower the ambient temperature of the protector 56. Accordingly, sincethe protector 56 is cooled by gas from the desuperheater coil and it ispositioned in the lower (and cooler) portion of the motor compartment,the cut-out temperature may be set relatively low. Thus, if the flow ofcompressed refrigerant gas decreases or stops due to a locked rotorcondition or a nonstart condition for example, the temperature of thestator winding 34 will immediately begin to rise. Since the cutouttemperature point of the protector 56 is set relatively low and thecompressed refrigerant gas from the desuperheater coil 48 is no longercooling the protector, the protector will operate in a minimum amount oftime to disconnect the motor from the power source, as noted in greaterdetail below.

The overload protector 56 is normally connected in series with the motor28 and its energizing source as noted above. More specifically, as shownin FIG. 2, the motor 28 is connected between a pair of input terminals58 and 60 which, in turn, are connected to the respective terminals of asource of energy 62. The overload protector 56 is connected between oneterminal of the motor 28 and the input terminal 58. Accordingly, themotor current flows through the overload protector 56. The overloadprotector 56 operates on an additive basis (i.e., it senses heatgenerated by the motor current flowing through it as well as the heatgenerated by the winding) so that it monitors the current flowingthrough the motor 28 in addition to the ambient temperature of theprotector 56. Hence, the overload protector will operate to disconnectthe motor from the energizing source if the current drawn by the motorexceeds an overload value or if the temperature of the protector (and,therefore, the winding 34) rise to an overload point or any combinationof the two.

As a result of positioning the overload protector 56 adjacent to thedischarge end of the desuperheater coil 48 and adjacent to the bottom ofthe motor compartment 24, the ambient temperature of the overloadprotector 56 will be relatively low, as noted above. Therefore, thecurrent drawn by the motor 28 may be increased above normal withoutcausing the overload protector to operate as long as the current doesnot generate heat in excess of that which would cause the overloadprotector to operate. Thus, the motor 28 can run at lower terminalvoltages since larger currents can be tolerated by the system. Hence,the compressor having the overload protector of the present invention isideally suited for use during brown-out periods, when the terminalvoltage is decreased. This is an extremely important consideration sincebrown-outs lie, decreased terminal voltage) most likely occur duringsummer months. However, this is precisely when the maximum demands areplaced on refrigeration systems of the type under consideration. Thepres ent invention therefore provides ideal protection for thecompressor since it permits substantial low voltage operation at highload without taking the refrigeration system out of service.

Accordingly, a refrigerant compressor with an overload protector hasbeen provided which has a faster response to overload conditions andwhich permits the compressor to operate at high load and relatively lowvoltage conditions.

While a preferred embodiment of the invention has been shown anddescribed herein, it will be obvious that numerous omissions, changesand additions may be made in such embodiment without departing from thespirit and scope of the present invention.

What is claimed is:

l. A compressor for a refrigeration system comprising:

a. a sealed housing having a compressor unit compartment in the lowerportion and a motor compartment in the upper portion thereof;

b. a compressor unit disposed within said compressor unit compartment ofsaid housing;

c. a motor disposed in said motor compartment of said housing andconnected in driving relation ship with said compressor unit;

, i. said motor comprising a rotor,

ii. and a stator provided with a winding having a bottom portionpositioned adjacent to the bottom of said motor compartment;

d. a compressor inlet for introducing refrigerant gas discharged fromthe refrigeration system into said compressor unit;

e. conduit means for providing a path for the flow of compressedrefrigerant gas from said compressor unit into said motor compartment;

f. a housing outlet providing for the discharge of compressedrefrigerant gas from said housing back to said refrigeration system;

g. and thermally operated switch means mounted adjacent to the bottom ofsaid motor compartment and connected in electric circuit with said motorfor disconnecting said motor from a source of potential when said switchmeans senses a temperature above a preselected value.

2. A compressor as in claim 1, in which said switch means is mounted onthe bottom portion of said stator winding in heat exchangingrelationship therewith.

3. A compressor as in claim 2, in which said conduit means comprises adesuperheater coil having an inlet opening connected with saidcompressor unit and an outlet opening positioned adjacent to said bottomportion of said stator winding.

4. A compressor as in claim 3, in which said switch means comprises athermostatic switch positioned in the path of flow of compressedrefrigerant gas from said desuperheater coil outlet opening.

5. A compressor as in claim 4, in which said housing comprises adischarge tube in the upper portion of said housing for dischargingcompressed refrigerant gas back into the refrigeration system, wherebycompressed refrigerant gas flows upwardly over said motor.

6. A compressor as in claim 1, in which said switch means generates heatin accordance with the motor current flowing therethrough, and saidswitch means senses temperatures due to the heat generated by thecurrent flowing therethrough and the heat of said stator winding.

1. A compressor for a refrigeration system comprising: a. a sealedhousing having a compressor unit compartment in the lower portion and amotor compartment in the upper portion thereof; b. a compressor unitdisposed within said compressor unit compartment of said housing; c. amotor disposed in said motor compartment of said housing and connectedin driving relation ship with said compressor unit; i. said motorcomprising a rotor, ii. and a stator provided with a winding having abottom portion positioned adjacent to the bottom of said motorcompartment; d. a compressor inlet for introducing refrigerant gasdischarged from the refrigeration system into said compressor unit; e.conduit means for providing a path for the flow of compressedrefrigerant gas from said compressor unit into said motor compartment;f. a housing outlet providing for the discharge of compressedrefrigerant gas from said housing back to said refrigeration system; g.and thermally operated switch means mounted adjacent to the bottom ofsaid motor compartment and connected in electric circuit with said motorfor disconnecting said motor from a source of potential when said switchmeans senses a temperature above a preselected value.
 2. A compressor asin claim 1, in which said switch means is mounted on the bottom portionof said stator winding in heat exchanging relationship therewith.
 3. Acompressor as in claim 2, in which said conduit means comprises adesuperheater coil having an inlet opening connected with saidcompressor unit and an outlet opening positioned adjacent to said bottomportion of said stator winding.
 4. A compressor as in claim 3, in whichsaid switch means comprises a thermostatic switch positioned in the pathof flow of compressed refrigerant gas from said desuperheater coiloutlet opening.
 5. A compressor as in claim 4, in which said housingcomprises a discharge tube in the upper portion of said housing fordischarging compressed refrigerant gas back into the refrigerationsystem, whereby compressed refrigerant gas flows upwardly over saidmotor.
 6. A compressor as in claim 1, in which said switch meansgenerates heat in accordance with the motor current flowingtherethrough, and said switch means senses temperatures due to the heatgenerated by the current flowing therethrough and the heat of saidstator winding.